Lamella separators, or settlers, provide for relatively high flow rate separation of liquids and solids by utilizing a plurality of inclined plates forming a plurality of inclined channels into which a liquid feed containing suspended solid material, for example, is introduced at a selected region of each of the channels. Clear liquid is thereupon removed from one end of the channels, while the solid material which collects on the lower surface of each of the channels ultimately settles at the opposite end of each of the channels and, thence, at a common settling tank from which it can thereupon be removed. The build-up of solids can be appropriately monitored, if desired, at the settling tank and when the build-up reaches an appropriate level, the solid material is removed by suitable pumping means. The solids, or solid material, as referred to here, at the settling tank and along the lower surfaces of each channel is in the form of a concentrated slurry. In addition to rapid sedimentation, such structures are relatively compact and substantially reduce the spatial requirements in comparison with a conventional settling basin or clarifier so that a high capacity output per unit volume is achievable.
Typical structures and the operation thereof utilizing inclined channels of this general type are discussed, for example, in U.S. Pat. Nos. 1,190,863; 1,746,156; 1,825,550; 3,494,475; 3,552,554; and 2,573,615. Other descriptions of separators of the lamella type can be found in the articles: "Lamella Sedimentation: A Compact Separation Technique," by B. Forsell and B. Hedstrom, Journal WPCF, Vol. 47, No. 4, Apr. 1975, pages 834-842; "The Lamella Separator; A Novel High Rate Sedimentation Device for Water Treatment Plants" (G. P. Souther and B. Forsell, Proceedings of the 32nd International Water Conference, Engineers Society of Western Pennsylvania, Pittsburgh, pages 180-182 (1971)); and "The SALA Lamella Thickener," SALA Information, published by SALA INTERNATIONAL, Sala, Sweden.
While such structures can operate effectively, particularly in comparison with a conventional settling basin or clarifier, a problem which has arisen with presently available lamella separator designs is that the clear liquid output thereof is often found to be contaminated with the solid material that is present in the feed liquid. Such contamination results from a mixing of the stream of clarified liquid with the feed stream containing the solid material and the entrainment of the contaminated clarified liquid by the clear liquid output. Contamination is normally further aggravated by the manner in which such present day devices are fed and controlled, the operation thereof leading to a reverse flow of the solid-containing feed liquid in the parallel channels, such reversal enhancing the contamination of the overflow or clear liquid output. Up to now no really effective method for substantially reducing such undesired contamination of the clear liquid output under such conditions has been successfully devised.